FR2828549A1 - Pre-stressed concrete pipe repair procedure consists of winding pre stressing wires round excavated portions in trench and back-filling - Google Patents

Abstract

The procedure consists of digging out a trench to expose a length of damaged pipe, making an excavation (8) under a first portion of the pipe centred on a joint (5) between two pipe sections (2, 3, 4), winding, tensioning a sleeved pre-stressing wire round the pipe, and back-filling with earth and compacting before moving on to the next portion. The excavated portions (6, 7) of the pipe have a length equivalent to half a pipe section, and the pre-stressing wires are wound round them from a pipe section joint outwards and spaced at about double the normal spacing before tensioning.

Description

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PIPE REPAIR PROCESS
The present invention relates to a method for repairing buried pipes.

 More particularly, the invention relates to a method for repairing pressurized fluid transport pipes formed by joining end-to-end segments of prestressed concrete pipe.

 These pipes belong for example to a water supply network. In their most common form, these pipes consist of an end-to-end assembly of pre-stressed concrete pipe segments, with a diameter varying from approximately 0.5 m to 6 m. The water circulates there under a pressure which can go up to about twenty bars. These concrete pipe segments may have an inner metal coating (liner). It is however not designed to withstand the pressure forces due to the fluid in circulation. These efforts are taken up by the prestressing of the concrete, carried out by means of wires wound in a spiral outside the concrete core of the pipe segment. During the prefabrication of this segment, its concrete core is rotated around its axis to receive the wire which is braked to be tensioned. This wire is then protected against corrosion by spraying an additional layer of concrete or mortar over a few tens of millimeters.

 Despite this protective layer and the passivation of the steel constituting these prestressing wires, it sometimes happens that the prestressing wires are the site of corrosion which generally leads to degradation of the protective coating, and therefore to an acceleration of the phenomenon, which can cause a break in the wires and therefore a structural weakening of the pipe, or even its break under the effect of the pressure of the circulating fluid.

 After detecting the incident on one or more segments by preventive methods (by acoustic detection in particular), the traditional methods consist first of excavating the material (sand, earth or the like) surrounding the deteriorated segments, then either to replace purely and simply the segments in question, which requires emptying the supply network beforehand, hence considerable inconvenience for the operation of the network, ie repairing the external surface of the

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 conduct, when the latter has not yet yielded.

 These known repair methods have the disadvantage of not taking into account the following operating constraints: - the excavation of the ground surrounding a pipe under fluid pressure presents a risk on the one hand for the safety of the workers, and on the other hand for the good mechanical strength of the joints between the segments, these joints being unable to work in bending and very little in shearing; - do not introduce additional deformations or stresses on the pipe during the repair; - the return of the seat to the ground after repair is necessary to avoid differential settlement; - obtaining a high level of protection for new prestressing reinforcements; - the durability of the old concrete and mortar found under the new reinforcement must be obtained; - the profile of the prestressing along the pipe must be optimized.

 The object of the present invention is in particular to improve the safety and reliability of the methods for repairing such pipes.

 According to the invention, a method of repairing a pipe for supplying a pressurized fluid composed of a succession of buried pipe segments made of prestressed concrete, comprises the following steps: - making a trench to clear a length of the driving ; - carry out a first excavation in the trench, under a first portion of the pipe substantially centered on a junction between two adjacent segments; - Put in place and tension at least one prestressing reinforcement around the first portion of the pipe; - fill the first excavation with soil material and compact said material; - carry out a second excavation in the trench, under a second portion of the pipe adjacent to the first portion and included in a single segment;

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 - Put in place and tension at least one prestressing reinforcement around the second portion of the pipe; - fill the second excavation with soil material and compact said material.

 Thanks to these provisions, it is possible to restore a damaged area of the pipe while respecting the technical constraints associated with this type of structure.

 In preferred embodiments of the invention, it is optionally possible to have recourse to one and / or the other of the following arrangements: the first and second portions of the pipe have a length substantially equal to half - length of pipe segment; - there are reinforcements with regular spacing along the first portion of the pipe, tensioning one reinforcement out of two from the junction towards the ends of the first portion by spacing the reinforcements about twice the value of regular spacing, then the remaining reinforcements are tensioned while returning towards the junction; - there are reinforcements with regular spacing along the second portion of the pipe, tensioning one reinforcement out of two from the ends towards the middle of the second portion, spacing the reinforcements about twice the value of l 'regular spacing, then the remaining reinforcements are tensioned, returning towards the ends; - At the ends of a repaired area of the pipe, there are placed and tensioned reinforcements around the pipe, with a greater spacing than in said first and second portions; - To compact the soil material in one of the excavations, two shoes are positioned below the pipe, on either side of the soil material filling the excavation and parallel to the pipe, by placing a connection system between the hooves, and the connecting system is actuated to bring the hooves closer to each other and compress said soil material; to facilitate compaction, we can introduce

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 needles in the interval between said shoes, and vibrating these needles during actuation of the linkage system; - The connection system comprises at least two metal strands connected to one of the shoes and passing through the other shoe, the actuation consisting, using at least one jack, of pulling on the ends of the strands which protrude of said other shoe by pressing against it; - Before filling each excavation under a portion of the pipe, the reinforcement put in place around said portion is carried out up to a tension representing a fraction of a specified prestressing value; after having filled said excavation and compacted the soil material, a partial backfilling of the trench is carried out in line with said portion so as to leave visible reinforcement blocking devices, an additional tension is applied to the reinforcements up to the specified prestressing value then the backfilling of the trench is completed; advantageously, the additional tension can be applied gradually during backfilling; - the reinforcements used are individually sheathed prestressing strands.

 Other features and advantages of the invention will appear during the following description of one of its embodiments, given by way of non-limiting example, with reference to the accompanying drawings, in which: - Figure 1 is a elevation view of a trench made in a first step of a method according to the invention for repairing a damaged pipe; - Figures 2 and 3 are elevational views illustrating the process of setting up and tensioning reinforcements around portions of the pipe shown in Figure 1; - Figures 4 and 5 illustrate a process of additional tensioning of the frames of Figures 2 and 3; - Figure 6 is an elevational view of one end of the repaired area of the pipe;

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 - Figure 7 is a top view of a series of consecutive frames provided with their anchors; and - Figure 8 is a cross-sectional view of a portion of the pipe, under which is installed compression device of the soil.

 In Figure 1, there is shown a buried pipe 1 formed by a succession of pipe segments 2, 3, 4 assembled end to end.

 Figure 1 shows a certain length released by digging a trench in the ground. In this length, the pipe 1 is damaged, its skin having defects D previously detected by a known method, for example an acoustic method. Detection is not necessarily very precise. In practice, we will be able to advance the trench along the pipe: after having uncovered a first length of the pipe, we proceed to repairs from one end of the trench, and after having started backfilling at this end , we continue to dig the trench at the other end. This can be progressed until the exposed pipe segments no longer have any apparent defects.

 Digging the trench consists in removing the soil material on each side of the pipe 1 over a width sufficient to allow the intervention of human operators. The depth of the trench is slightly greater than that of the base of the pipe. However, care is taken not to remove the soil material present just below the pipe, so as to support the weight of the pipe loaded with water.

 The repairs carried out according to the invention do not generally require draining the pipe. However, it may be prudent to reduce the pressure of the circulating fluid somewhat, given the removal of the ground around the pipe in the damaged areas, which no longer helps to counterbalance the internal pressure. The reduced pressure is calculated based on factors such as the topology of the ground, the total length of the trench, the nature of the defects found, etc. The reduction is made by working on the installations upstream of the area to be repaired.

 Each of the pipe segments consists of a concrete core, a

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 diameter varying from approximately 0.5 m to 6 m, with or without an internal metal liner, and with an average unit length of approximately 7.5 m for example.

 These segments 2, 3, 4 are intended for conveying pressurized water, of the order of approximately 20 bars, and are buried or sanded for the most part or entirely. In this way, the surrounding soil exerts a back pressure on the outer walls of the segments 2, 3, 4.

 To improve the resistance of these segments to fluid pressure, prestressing wires are wound in a spiral in one or two layers on their outer face and tensioned during their winding. An additional layer of mortar or sprayed concrete covers these prestressing wires to protect them from corrosive agents possibly present in the soil.

 Each of the joints 5 between the segments 2,3, 4 is formed by fitting a straight end of one of the adjacent segments into a widening provided at the end of the other segment, a sealing mortar being applied along the circumference of the joint. Line 1 thus constitutes a very rigid assembly which does not allow bending or shearing forces at the joints.

 Corrosion of the prestressing wires, following the penetration of aggressive agents into the protective mortar layer, can lead to the breaking of one or more metallic wires. These ruptures are generally grouped in points of preferential penetration of aggressive agents, and lead to delamination and crumbling of the protective mortar layer, under the effect of shearing. These delaminations are the apparent defects D, which make repair necessary.

 To repair the pipe according to the invention, an additional prestress is installed outside the pipe, using reinforcements 12 arranged around the pipe and distributed along the repaired area. These reinforcements are advantageously prestressed strands, and preferably individually sheathed strands, which improves their resistance to corrosion.

 Before installing these strands 12, the damaged area or areas should be cleaned up by mechanical treatment (brushing, hammering,

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 pickling ...), possibly supplemented by a chemical treatment, in particular by a corrosion inhibiting agent. After these treatments, mortar is reapplied on the areas that have been scraped in order to equalize the surface of the pipe.

 To put the reinforcement around the pipe 1, it is necessary to make excavations under the pipe. To avoid this inducing undesirable longitudinal bending or shearing stresses at the joints, excavations are judiciously located.

 We distinguish for this two types of portions which follow one another along the pipe (Figures 2 and 3): - first pipe portions 6 centered on the joints 5 between the pipe segments; - Second pipe portions 7 inserted between the first portions 6 and each included in a single pipe segment. These second portions 7 are centered on the midpoints of the segments.

 The length of these portions 6,7 is of the order of half the length of a segment 2,3, 4. By way of example, with the abovementioned segments of 7.5 m, the first portions 6 can be 3.5 m and the second portions 7 4 m.

 Firstly, an excavation is carried out in the trench under one of the first portions 6. After clearing of the ground located under the pipe, we proceed to any required remediation work, then the prestressing strands 12 are put in place. symmetry of the excavation on either side of the plane of the joint 5 and the limited extent of the overhang on each side of this joint (approximately a quarter of the length of a segment) makes it possible to minimize the efforts unwanted bending and shearing that occurs at the joint. As drawn in FIG. 2, it is possible to form excavations 8 at the same time under several of the first portions 6.

 The strands 12 are engaged in the excavation so as to surround the pipe 1 over one or two turns. They are attached to the upper side of the pipe using a blocking device 11 (FIG. 7) adapted to receive the two ends of one or more of the strands 12.

 In the embodiment illustrated in Figure 7, each strand 12 makes a single

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 turn around the pipe, and the blocking devices 11 are generally X-shaped, with two curved channels intended to each receive one end of a strand. Each of its channels has a frustoconical mouth suitable for receiving a frustoconical anchoring jaw for blocking the end of the strand. To tension it, put the jaws in place and pull on one of the protruding ends of the locking device 11 (or symmetrically on the two ends), using an actuator with a jack, pushing the bit towards the frustoconical mouth.

 When using individually sheathed strands, preferably with a protective material such as grease inside the sheath, it is advisable to strip the ends of the strand which will be gripped by the frustoconical jaws before installing the latter. To complete the protection against corrosion, it is possible to use blocking devices 11 made of steel coated with a protective layer of plastic. After the final tensioning of the strand, its ends protruding from the jaws can be cut and plastic plugs placed over these ends, which allows a thickness of plastic material (for example high density polyethylene) on all prestressing members susceptible to corrosion.

 Alternatively, one can make two turns of the pipe with each strand and use blocking devices such as that described in French patent application 01 03537.

 In Figure 2, there is shown a series of strands 12 placed around the pipe segments and tensioned symmetrically to avoid asymmetrical stresses on the joints.

 In general, the structural calculation defines a preload requirement per unit of length, which determines on the one hand a density of strands, in number of turns per meter of pipe, and on the other hand a tension setpoint of each strand. The strands 12 are placed with a substantially constant spacing between two neighboring strands, corresponding to the inverse of the number of turns per meter of pipe. As shown in FIG. 7, when this spacing is relatively small, the anchoring devices 11 can be staggered on the upper side of the pipe, to have room for them

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 install and then equip them with the actuator.

 Figures 2 to 5 illustrate a possible course of the operations of setting up and tensioning the prestressing frames 12 around the pipe. It will be noted that these operations can also be carried out according to various other sequences.

 The tensioning procedure illustrated in Figure 2 is applied to reach only a fraction (for example 50%) of the voltage setpoint. This procedure is for example the following for each of the first portions 6: - a strand is first stretched over two strands in a forward movement from the joint 5 towards the second adjacent portions 7; then - the remaining strands are stretched in a return movement while returning to the joint 5.

 These back and forth movements are illustrated by the arrows f1, f2 in FIG. 2.

 The next phase, illustrated by the cross section of FIG. 8, consists of filling the excavation formed under the first portion 6 with the soil material 9 which has been previously removed, then compacting this material under the pipe to form a heel. locally restoring the seat of the pipe.

 The compaction of these heels is advantageously carried out using two shoes 13,14 positioned below the pipe on each side of the material 9 with which the excavation 8 has been filled. These shoes are oriented parallel to the pipe and linked together by a connection system 15-17 allowing them to be brought together by compressing the material 9.

 In the example of FIG. 8, the connection system comprises metallic strands 15, for example prestressing strands. Each of these strands 15 is connected to one of the shoes 14, for example using a spun sleeve 17 bearing against the edge of an orifice provided in this shoe 14 and crossed by the strand 15. Its other end passes through the opposite shoe 13 where a jack actuator 16 is positioned. This actuator 16 bears against this shoe 13 and is activated to pull on the protruding end of the strand 15.

 To improve the compaction of the material 9, the shoes 13 are added,

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 14 a vibrating system of the kind commonly used for vibrating concrete. This system includes vibrating needles 19 which penetrate the compacted layer of ground by crossing the shoes 13,14. The vibrations transmitted by these needles during the activation of the actuators 16 ensure a reduction in the void rate of the material 9 and therefore an improvement in its compaction.

 After restoring the foundation of the pipe 2 under the first portions 6, other excavations are carried out in the trench, under the second portions of pipes 7 adjacent to the first portions 6 which have just been repaired.

 The operating mode is similar to that described above for the first portions 6. The surface of the pipe in the area of the second portion 7, updated by excavation 8, is cleaned if necessary, then the reinforcements 12 are placed with the required spacing. The tensioning procedure illustrated in Figure 3 is applied to reach the same fraction (for example 50%) of the voltage setpoint. This procedure is as follows for one of the second portions 7: - a strand is first stretched over two strands in a forward movement directed from the ends of the portion 7 towards its middle; then - the remaining strands are stretched in a return movement returning towards the ends.

 The excavation 8 is then filled with soil material which is compacted in the same manner as above.

 This procedure is repeated step by step over a certain length of pipe in the trench. At this stage, the strands 12 positioned around the first and second portions 6, 7 of the pipe are only tightened to a certain percentage of the set value, which ensures their adequate positioning around the pipe and a first phase of prestressing.

 The tensioning can be completed later, after a partial backfilling of the trench, as illustrated by Figures 4 and 5. The backfill height is chosen so as to leave sufficient access to the blocking devices to install the actuator in cylinder used for tensioning

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 the strands 12. the additional tensioning, up to the set value, can be carried out in a sequence similar to the first tensioning, with back and forth movements in each of the first and second portions 6,7. These back and forth movements, where one armature out of two is tensioned, are illustrated by the arrows f 1 and f'2 in FIG. 4 (first portions 6), and by the arrows f'3 and f'4 on the Figure 5 (second portions 7).

 When these tensioning operations are completed, complete backfilling of the trench is carried out.

 Alternatively, the additional tension is gradually applied during backfilling. This can be done in several successive backfilling steps up to the level illustrated in FIGS. 4 and 5, increasing at each step the tension applied to the strands 12.

 To optimize the profile of the prestress in the vicinity of the end of the repaired area or of another singularity, it is possible to locally increase the spacing between the strands 12 along the pipe compared to the spacing adopted in the portions 6 and 7 previously described, as shown in FIG. 6.

Claims (11)

CLAIMS 1. Method for repairing a pressurized fluid supply pipe (1) composed of a succession of buried pipe segments (2, 3, 4) made of prestressed concrete, comprising the following steps: - making a trench to release a length of the pipe (1); - Make a first excavation (8) in the trench, under a first portion of the pipe (6) substantially centered on a junction (5) between two adjacent segments; - Put in place and tension at least one prestressing frame (12) around the first portion of the pipe; - fill the first excavation with soil material (9) and compact said material; - Carry out a second excavation in the trench, under a second portion of the pipe (7) adjacent to the first portion and included in a single segment; - Put in place and tension at least one prestressing reinforcement (12) around the second portion of the pipe; - fill the second excavation with soil material and compact said material. 2. Method according to claim 1, wherein the first and second portions of the pipe (6,7) have a length substantially equal to half a length of pipe segment. 3. Method according to claim 1 or 2, in which there are reinforcements (12) with regular spacing along the first portion of the pipe (6), one tensioning one reinforcement out of two from the junction (5 ) towards the ends of the first portion, spacing the reinforcement approximately twice the value of the regular spacing, then tension the remaining reinforcement by returning to the junction. 4. The method of claim 3, wherein there are reinforcements (12) with regular spacing along the second portion of the <Desc / Clms Page number 13>  pipe (7), tension one reinforcement out of two from the ends towards the middle of the second portion, spacing the reinforcements approximately twice the value of the regular spacing, then tension the remaining reinforcements in returning to the ends. 5. Method according to any one of the preceding claims, in which, at the ends of a repaired area of the pipe (1), reinforcements (12) are placed and tensioned around the pipe, with more spacing important only in said first and second portions (6, 7). 6. Method according to any one of the preceding claims, in which, to compact the soil material (9) in one of the excavations (8), two shoes (13,14) are positioned below the pipe (1), on either side of the soil material filling the excavation and parallel to the pipe (1), by placing a connection system (15-17) between the shoes, and the connection system is actuated to bring the shoes together. to each other and compress said soil material. 7. The method of claim 6, wherein needles are introduced (19) in the interval between said shoes (13,14), and these needles are vibrated during actuation of the connecting system (15-17). 8. Method according to claim 6 or 7, in which the connection system comprises at least two metal strands (15) connected to one of the shoes (14) and passing through the other shoe (13), the actuation consisting, using at least one jack (16), pull on the ends of the strands which protrude from said other shoe while pressing against it. 9. Method according to any one of the preceding claims, in which before filling each excavation with a portion (6,7) of the pipe, the tensioning of the reinforcements (12) placed around said portion is carried out until '' at a tension representing a fraction of a specified prestressing value, and in which after filling said excavation (8) and compacting the soil material (9), a backfill is carried out <Desc / Clms Page number 14>  partial of the trench to the right of said portion so as to leave apparent reinforcement blocking devices (11), an additional tension is applied to the reinforcements up to the specified prestressing value, then the backfilling of the trench is completed. 10. The method of claim 9, wherein the additional tension is gradually applied during backfilling. 11. Method according to any one of the preceding claims, in which said reinforcements are individually sheathed prestressing strands (12).